The mathematical method is the "response spectrum modal analysis". Before calculation, the user of ERDBEBEN has to idealize the structure with finite elements and to calculate its eigenfrequencies with the program NASTRAN (level 15). The superposition of the eigenforms will be done by the "root mean square method".

The length of the arrays can be variable (parameter card). Only the number of the different types of finite elements cannot be more than 5. The program calculates the element forces only for beam and spring elements.